The invention is directed to a process for recovering acids from mixtures containing them, in particular organic acids, such as acids produced by fermentation in a fermentation broth.
Organic acids (viz. acids characterized by a carboxyl (—COOH) group), such as lactic acid, citric acid, succinic acid, cinnamic acid and amino acids, are useful base chemicals that may be produced by fermentation of organic material, in particular from material containing sugars, or compounds containing sugar groups, such as cellulose.
To recover the product, generally use is made of an extracting agent, in particular an organic extracting agent, such as tertiary or quaternary amines. By contacting the fermentation broth with the extractant, the product that is dissolved in the broth is transferred from the broth to the extractant, by which the product is concentrated in the extractant. Subsequently the product is removed from the extractant by extracting it back therefrom. In this way, further concentration of the product is obtained. In case the product is an organic acid, back extraction may e.g. be carried out by addition of an alkaline solution to the loaded extractant. As a result, the interaction between the extractant and the product is broken, and the anion of the acid is transferred to the alkaline solution phase. This method requires the continuous replenishing of the basic solution. Subsequently, an acid, in particular an inorganic acid, such as H2SO4, is added to the alkaline solution, which results in formation of the product acid so that the product acid can be obtained. An (inorganic) salt is obtained as a by product, which usually is disposed of as a waste.
The disadvantage of this process for back-extraction of acids from a fermentation broth or other type of mixture, is that a considerable stream of waste is produced in the form of a salt, such as gypsum. The present invention seeks to overcome this and other disadvantages.